In a wide mouthed container for paint, wax and the like, a mouth portion thereof comprises an external wall and an internal wall that is formed to be lower than and on the inside of the external wall past an annular groove. A lid is fitted to an inner side surface of the mouth portion formed by the internal wall, and a rim of the lid is fitted to the inside of the external wall, so that the container is kept sealed. The lid can be easily removed by inserting a tip of a screwdriver and the like between the external wall and the rim of the lid, and pushing down a grip of the screwdriver supported at the external wall.
Conventionally, most of such wide mouthed containers with a double-walled mouth portion are made of metal, but those of synthetic resins are newly manufactured by employing the injection molding method, injection blow molding method and the like. However, such molded articles cannot be thinly formed in the body portion thereof, and are poor in strength as compared with those of metals, which gives rise to a problem in that they are easily broken when dropped.
Approaches to the problem are made in which paint containers and the like are manufactured by employing the injection stretch blow molding method that enables resins to be reinforced by biaxial stretching. A paint container disclosed in WO97/19801 is manufactured by the steps of: injection molding a preform consisting of a large-diameter mouth portion comprising a belt shaped external wall and an internal wall which is formed to be lower than and on the inside of the external wall via a joint portion past an annular groove, and a body portion having a bottom which is molded extending from the underside of the internal wall; transferring the preform to a blow mold for molding a paint container; and stretch blowing the preform below the body portion thereof from the underside of the internal wall.
In the disclosed injection stretch blow molding, the external and internal walls of the mouth portion cooled and solidified are held between a mouth forming mold and a core mold while heated portions below the body portion thereof is axially stretched. At almost the same time, the body portion is also air blown to a skirt portion which is projectingly formed on the underside of the external wall, so that the unstretched joint portion and an upside of the body portion which is blown and stretched into shoulder-shape are integrated.
In a paint container according to the ways described above, the body portion and bottom thereof are thin and biaxially oriented by the stretch blowing. Therefore, as compared to those manufactured by injection molding or injection blow molding, such a container is light in weight and improved in falling strength, and may be improved in gas barrier capability depending on the material resins.
However, in the stretch blowing according to the aforesaid prior art, no supporting part for the aforesaid joint portion is provided between the skirt portion and the internal wall; therefore, axial tensile stresses concentrate to the joint portion in stretch blowing, the joint portion is drawn downwardly from a corner of the skirt portion and deformed, and strains occur in the internal wall. This gives rise to a problem in that the molding accuracy is decreased in a mouth end edge and an inner surface of the internal wall which are to be a fitting edge and an inner side surface of the mouth portion, and thus the fit with the lid is deteriorated and the sealing capability lost.
As the span of the joint portion gets longer, the strains in the internal wall caused by the axial stretching come to the front. This can be improved by reducing the span, which, however, limits the radial expansion of the body portion. Thereby the body portion is formed thicker in the upper part thereof and thinner in the lower, resulting in unevenness of the wall thickness, which lowers the buckling strength of the body portion. In such cases, containers at the bottom may be deformed by load when a plurality of containers are piled up.
Like an injection blow molded paint container disclosed in the Japanese Patent Laid-Open Publication No. Sho 57-77439, ribs may be provided to support the joint portion. However, such ribs as described therein being formed across the external and internal walls cause a difference between ribbed and non-ribbed portions in stretched state. As a result, irregularity tends to be induced on the inner surface of the internal wall to which a lid is fitted.
Since touching to and located between the external and internal walls, the ribs take time to be cooled and solidified completely enough for bearing the tensile stress. On the other hand, the preform has to be released from the molds while the portions below the body portion still have a required amount of heat for stretch blowing. Therefore, the support by providing the ribs has not always been an effective approach for injection stretch blow molding.
Through the perpetual studies of the inventor of the present invention concerning the prevention of the aforesaid tensile deformation of the internal wall caused by the axial stretch, it has been found that even though ribs are employed for supporting the joint portion, conventional defects can be avoided depending on the way of forming ribs. That is, even in a wide mouthed container such as an injection stretch blow molded paint container, the inventor has found that it is possible to prevent the tensile deformation of the joint portion resulting from the stretching, as well as to avoid the convexo-concave deformation of the inner surface of the mouth portion caused by the conventional ribs and to finish the cooling and solidification of the ribs in a short period of time.
It is thus an object of the present invention to provide an injection stretch blow molded wide mouthed container of large diameter for a paint container and the like in which the problem of the strains in the internal wall resulting from the tensile deformation of the aforesaid joint portion is solved by the introduction of the reinforcing means using small ribs, and, despite of being made of synthetic resins, the body portion is formed thinly and is improved in falling strength because of the biaxial orientation.
In addition, the present invention is to provide an injection stretch blow molded wide mouthed container of large diameter for a paint container and the like in which the body portion and the external wall of the mouth portion are formed into side faces on the same level, like conventional paint tins and the like. By this means, even if the radial expansion of the body portion is limited, the employing of a preform of certain shape in cross-section allows the body portion to be molded without irregular in wall thickness, thereby enabling a plurality of the wide mouthed containers to be piled up.
Furthermore, the present invention is to provide an injection stretch blow molded wide mouthed container of large diameter for a paint container and the like in which a handle can be rotatably mounted across both sides of the mouth portion by utilizing the external wall, and the lid can be prevented from popping-out caused by a reaction in removing the lid, an increase in pressure inside the container, or the like.